1. Field of the Invention
The invention relates to a fuel-outflow check valve that is provided in a ventilation passage extending between a fuel tank and a canister in a vehicle to prevent fuel from flowing out from the fuel tank to the canister when the vehicle has been turned over, when the vehicle is cornering, and the like.
2. Description of the Related Art
In a vehicle (e.g., motor vehicle), a fuel tank is provided which stores fuel supplied to the combustion chambers of the engine of the vehicle. In the fuel tank, a ventilation passage is formed via which air enters and leaves the fuel tank as the amount of fuel in the fuel tank increases or decreases. The ventilation passage is the passage via which the interior of the fuel tank and a canister communicate with each other. If the ventilation passage is provided alone, when the vehicle has been turned over, when the vehicle is cornering, or the like, fuel flows out of the fuel tank and reaches the canister via the ventilation passage and the canister is moistened by the fuel, which may critically damage the canister. To counter this, typically, a fuel-outflow check valve is provided in the upper side of the fuel tank. The fuel-outflow check valve is open in a normal state. When the vehicle has been turned over, when the vehicle is cornering, or the like, the fuel-outflow check valve is closed to prevent the outflow of air and fuel to the canister side.
FIG. 12 shows the structure of such a conventional fuel-outflow check valve. A fuel tank 1 mounted in a motor vehicle, or the like, stores fuel to be supplied to the engine of the motor vehicle. A fuel-outflow check valve A is provided in the upper side of the fuel tank 1. The fuel-outflow check valve A is constituted of a casing 2 that is inserted into the fuel tank 1, a float 3 disposed in the casing 2, a spring 4 urging the float 3 upward, a valve element 5 provided on the float 3, a ventilation passage 6 provided downstream of the valve element 5 and leading to a canister (not shown in the drawing), etc.
The casing 2 is a cylindrical container having a hollow structure with a lower opening. A float chamber 7 is formed within the casing 2. A valve seat 8 which the valve element 5 contacts is formed in the upper side of the float chamber 7. Vertical ribs 9 are formed on the inner peripheral face of the casing 2 so as to extend radially. The vertical ribs 9 serve to guide the vertical movement of the float 3. A bottom plate 11 is attached to the bottom of the casing 2. Lower ventilation holes 10 are formed in the bottom plate 11, and side ventilation holes 12 are formed in the side portion of the casing 2. Further, a flange 13 is formed on the upper side of the outer peripheral face of the casing 2. The casing 2 is attached on the fuel tank 1 via the flange 13.
In the fuel-outflow check valve A configured as described above, in a normal state, the float 3 is located at the lower position and thus the valve element 5 is away from the valve seat 8. In this state, fuel vapor in the fuel tank is brought to the canister. Meanwhile, when the vehicle has been turned over, when the vehicle is cornering, or the like, fuel enters the float chamber 7 and the float 3 is lifted up by the buoyant force, and so on, so that the valve element 5 contacts the valve seat 8. As such, the ventilation passage 6 is closed, preventing fuel from flowing toward the canister (For example, refer to Japanese Patent Application Publication No. 08-258577 (JP-A-08-258577)).
Meanwhile, in recent years, there has been an increasing trend of high-response vehicles. Such vehicles are subjected to a relatively large force when starting from standstill, when coming to a stop, when cornering, or the like. Therefore, if a conventional fuel-outflow check valve is used in such a high-response vehicle, there is a possibility that fuel enters the ventilation passage 6 before the valve element 5 closes the ventilation passage 6.